CN110446834B

CN110446834B - Spark ignition type internal combustion engine

Info

Publication number: CN110446834B
Application number: CN201880019093.9A
Authority: CN
Inventors: 青木秀马; 村中宏彰; 山口直宏; 和田好隆
Original assignee: Mazda Motor Corp
Current assignee: Mazda Motor Corp
Priority date: 2017-03-27
Filing date: 2018-02-27
Publication date: 2021-07-30
Anticipated expiration: 2038-02-27
Also published as: JP6515941B2; EP3584420A4; US10968817B2; CN110446834A; WO2018180129A1; JP2018162726A; US20200131978A1; EP3584420A1

Abstract

A crown surface (10) of a piston (5) is provided with a bulge section (31) including an intake-side inclined surface (34) and an exhaust-side inclined surface (35), and a cavity (40) is provided in the bulge section (31) at a position corresponding to an ignition plug, the intake-side inclined surface (34) and the exhaust-side inclined surface (35) being formed in such a manner that: the inclination angle of the exhaust side inclined surface (35) is smaller than that of the intake side inclined surface (34), and the difference in inclination angle between the intake side inclined surface (34) and the exhaust side inclined surface (35) is 4 degrees or more.

Description

Spark ignition type internal combustion engine

Technical Field

The present invention relates to a spark ignition internal combustion engine, and more particularly to a spark ignition internal combustion engine comprising: a crown surface of the piston is provided with a bulge portion, and a chamber is provided in a position corresponding to the spark plug in the bulge portion.

Background

The following techniques are known: in a spark ignition type internal combustion engine having a ridge type combustion chamber mounted in a vehicle such as an automobile, a crown surface of a piston is provided with a raised portion to increase a geometric compression ratio, and a chamber recessed downward is provided at a position corresponding to an ignition plug at the center of the raised portion. With this internal combustion engine, the timing at which the initial flame front after ignition of the spark plug interferes with the piston crown surface can be delayed. This improves flame propagation and improves fuel economy.

For example, patent document 1 discloses a spark ignition type internal combustion engine shown in fig. 17. An internal combustion engine 100 shown in fig. 17 includes a ridge-shaped combustion chamber 101, an intake passage 103 and an exhaust passage 104 formed in a cylinder head defining a top surface 102 of the combustion chamber 101, and an ignition plug 105 and a fuel injection valve 106 attached to the cylinder head. The ignition plug 105 is provided in the central portion of the top surface 102 (between the intake passage 103 and the exhaust passage 104). The fuel injection valve 106 is disposed at a position offset to the intake side with respect to the central portion of the top surface 102.

In the internal combustion engine 100 of patent document 1, a raised portion 111 is formed on a crown surface 108 of a piston 107 defining a bottom surface of a combustion chamber 101, and the raised portion 111 has an intake-side inclined surface 109 and an exhaust-side inclined surface 110 along a top surface 102 of the combustion chamber 101. A cavity 112 recessed downward is formed in the center of the ridge portion 111 at a position corresponding to the spark plug 105. Thus, even when the geometric compression ratio is 13 or more, the flame propagation property can be improved, and the fuel economy can be improved.

In a spark ignition internal combustion engine, a so-called helical air passage capable of generating tumble flow (longitudinal swirl) in a combustion chamber is sometimes used as an intake passage. In a spark ignition type internal combustion engine using a spiral type air passage, tumble flow which is dispersed as a piston approaches a compression top dead center (i.e., as a combustion chamber is narrowed) generates turbulence, thereby promoting combustion and improving fuel economy. As indicated by an arrow 113 in fig. 17, the tumble flows downward from the intake passage 103 and toward the exhaust side, and then changes direction along the inner circumferential surface of the cylinder and flows from the exhaust side to the intake side along the crown surface 108 of the piston 107. The tumble flows from the intake side to the exhaust side along the top surface 102 of the combustion chamber after the intake side changes direction upward along the inner circumferential surface of the cylinder.

However, the spark ignition type internal combustion engine using the piston having the bulge portion and the chamber as in patent document 1 has the following problems: when the tumble flow flows from the exhaust side to the intake side along the crown surface of the piston, the tumble flow is obstructed by the bulge portion, and the tumble flow is easily decelerated. The deceleration of the tumble flow is not preferable in terms of fuel economy because it reduces the turbulent flow energy generated by tumble flow breakup and reduces the combustion promoting effect.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 2010-14081

Disclosure of Invention

The invention aims to: in a spark ignition type internal combustion engine in which a crown surface of a piston is provided with a bulge portion and a chamber is provided at a position corresponding to a spark plug in the bulge portion, a tumble deceleration action on the crown surface of the piston is reduced, thereby improving fuel economy.

The spark ignition type internal combustion engine of the present invention to achieve the above object includes: a cylinder; a piston disposed in the cylinder so as to be capable of reciprocating; a cylinder head provided on the cylinder and forming a ridge-shaped combustion chamber together with an inner peripheral surface of the cylinder and a crown surface of the piston; and an ignition plug provided to the cylinder head so as to face the combustion chamber; wherein a crown surface of the piston is provided with a bulge portion having an intake side inclined surface and an exhaust side inclined surface along a top surface of the combustion chamber, a chamber depressed downward is provided at a position corresponding to the ignition plug in the bulge portion, the cylinder head is provided with an intake passage capable of generating tumble flow in the combustion chamber, and the intake side inclined surface and the exhaust side inclined surface are formed in such a manner that: the inclination angle of the exhaust side inclined surface is smaller than that of the intake side inclined surface, and the difference in inclination angle between the intake side inclined surface and the exhaust side inclined surface is 4 degrees or more.

Drawings

Fig. 1 is a schematic diagram showing the configuration of a spark ignition type internal combustion engine according to a first embodiment of the present invention.

Fig. 2 is a perspective view showing a piston, a fuel injection valve, and an ignition plug of the internal combustion engine.

Fig. 3 is a perspective view showing a distal end surface of the fuel injection valve.

Fig. 4 is a timing chart showing a fuel injection timing.

Fig. 5 is an explanatory diagram for explaining the spray of fuel injected from the fuel injection valve.

Fig. 6 is a perspective view of the piston.

Fig. 7 is a top view of the piston.

Fig. 8 is a sectional view of the piston taken along line Y8-Y8 of fig. 7.

Fig. 9 is a sectional view of the piston taken along line Y9-Y9 of fig. 7.

Fig. 10 is a sectional view of the piston taken along line Y10-Y10 of fig. 7.

Fig. 11 is an explanatory view for explaining the shape of the cavity provided in the ridge portion.

Fig. 12 is a perspective view of a piston of a spark ignition type internal combustion engine according to a second embodiment of the present invention.

Fig. 13 is a top view of a piston of the internal combustion engine.

Fig. 14 is a sectional view of the piston taken along line Y14-Y14 of fig. 13.

Fig. 15 is a sectional view of the piston taken along line Y15-Y15 of fig. 13.

Fig. 16 is a graph showing the relationship between the difference in inclination angle between the intake-side inclined surface and the exhaust-side inclined surface of the bulge portion and the turbulent energy.

Fig. 17 is a diagram showing a conventional spark ignition type internal combustion engine.

Detailed Description

Embodiments of the present invention will be described below with reference to the drawings.

[ first embodiment ]

Fig. 1 is a schematic diagram showing the configuration of a spark ignition type internal combustion engine according to a first embodiment of the present invention. Fig. 2 is a perspective view showing a piston, a fuel injection valve, and an ignition plug of the internal combustion engine. As shown in fig. 1 and 2, an engine 1, which is a spark ignition type internal combustion engine according to a first embodiment of the present invention, is a multi-cylinder gasoline engine in which a plurality of cylinders 2 are arranged in a row, and is mounted on a vehicle such as an automobile. The engine 1 includes: a cylinder block 3 having a cylinder 2 formed therein; a cylinder head 4 provided on the cylinder block 3 so as to cover the cylinder 2 from above. IN fig. 1 and 2, the intake side is denoted by "IN" and the exhaust side is denoted by "EX" (this is the same IN other figures).

A piston 5 is provided in the cylinder 2 so as to be capable of reciprocating. The piston 5 is connected to a crankshaft 6 rotatably supported at a lower portion of the cylinder block 3 via a connecting rod 7, and the reciprocating motion of the piston 5 is converted into the rotational motion of the crankshaft 6.

A ridge-shaped combustion chamber 8 surrounded by an inner peripheral surface 9 of the cylinder 2, a crown surface 10 of the piston 5, and a lower surface 11 of the cylinder head 4 is formed above the piston 5. The lower surface 11 of the cylinder head 4, which covers the combustion chamber 8, is a ceiling surface 12 formed in a ridge shape (a triangular roof shape) and has an intake-side inclined surface 13 and an exhaust-side inclined surface 14 inclined on the intake side and the exhaust side, respectively. The intake-side inclined surface 13 is formed so that the angle formed by it and the orthogonal surface orthogonal to the axial center 2a of the cylinder 2 is 23 degrees, and the exhaust-side inclined surface 14 is formed so that the angle formed by it and the orthogonal surface orthogonal to the axial center 2a of the cylinder 2 is 17 degrees.

The cylinder head 4 is formed with an intake passage 15 and an exhaust passage 16 that open on the intake-side inclined surface 13 and the exhaust-side inclined surface 14 of the head surface 12, respectively. Each cylinder 2 is provided with two intake ports 15 and two exhaust ports 16, and the two intake ports 15 and the two exhaust ports 16 are provided at intervals in a direction (axial direction of the crankshaft 6) orthogonal to the axial center 2a of the cylinder 2.

An intake passage 17 that supplies air to the combustion chamber 8 is connected to the intake passage 15, and an exhaust passage 18 that exhausts combustion gas (exhaust gas) from the combustion chamber 8 is connected to the exhaust passage 16. The exhaust passage 18 is provided with a catalyst device (not shown) having a catalyst for purifying exhaust gas.

The intake duct 15 opens in the top surface 12 of the combustion chamber 8 in a state of linearly extending obliquely upward from the combustion chamber 8 so as to generate a tumble flow (swirl flow) in the combustion chamber 8. As intake air is introduced from the intake passage 15, tumble flow as indicated by an arrow 19 in fig. 2 is generated in the combustion chamber 8. The tumble flows downward from the intake passage 15 toward the exhaust side, then changes direction along the inner peripheral surface 9 of the cylinder 2, and flows from the exhaust side toward the intake side along the crown surface 10 of the piston 5. The tumble flows in the direction that the intake side changes upward along the inner circumferential surface 9 of the cylinder 2, and then flows from the intake side to the exhaust side along the top surface 12 of the combustion chamber 8.

The cylinder head 4 is provided with an intake valve 20 and an exhaust valve 21 that open and close the intake passage 15 and the exhaust passage 16, respectively. The intake valve 20 is driven by an intake camshaft 22 coupled to the crankshaft 6 in an interlocking manner, and opens and closes the intake passage 15 at a predetermined timing so as to introduce air into the combustion chamber 8 in the intake stroke. The exhaust valve 21 is driven by an exhaust camshaft 23 linked to the crankshaft 6, and opens and closes the exhaust passage 16 at a predetermined timing so as to discharge exhaust gas from the combustion chamber 8 in the exhaust stroke.

The cylinder head 4 is provided with a variable valve gear, not shown. The variable valve gear changes the timing at which the intake valve 20 and the exhaust valve 21 open and close the intake passage 15 and the exhaust passage 16. The variable valve gear may open both the intake valve 20 and the exhaust valve 21 in the exhaust stroke. This is to discharge the residual exhaust gas by the intake air from the intake passage 15.

The intake valve 20 has a stem portion 20a and an umbrella portion 20b formed at a lower end portion thereof. The bottom surface of the umbrella portion 20b, that is, the umbrella portion bottom surface 20c, is formed so as to be orthogonal to the valve axis 20d, that is, the axial center of the valve stem portion 20a, and to be parallel to the intake-side inclined surface 13 of the top surface 12. That is, the bottom surface 20c of the umbrella part of the intake valve 20 is formed so that an angle formed by the bottom surface and an orthogonal surface orthogonal to the axial center 2a of the cylinder 2 becomes 23 degrees.

The exhaust valve 21 has a valve stem portion 21a and an umbrella portion 21b formed at a lower end portion thereof. The bottom surface of the umbrella part 21b, that is, the umbrella part bottom surface 21c is formed so as to be orthogonal to the valve axis 21d, that is, the axial center of the valve stem part 21a, and to be parallel to the exhaust side inclined surface 14 of the top surface 12. That is, the exhaust valve 21 is formed such that the angle formed by the bottom surface 21c of the umbrella part and the perpendicular surface perpendicular to the axial center 2a of the cylinder 2 becomes 17 degrees.

The cylinder head 4 is provided with: a fuel injection valve 24 that injects fuel into the combustion chamber 8; and an ignition plug 25 for igniting an air-fuel mixture containing fuel and air formed in the combustion chamber 8 based on the injection. The fuel injection valve 24 is provided so as to face the combustion chamber 8 at the peripheral edge portion on the intake side of the top surface 12. The ignition plug 25 is provided so as to face the combustion chamber 8 at a central portion of the top surface 12.

The ignition plug 26 is attached to the cylinder head 4 such that the electrode 25a at the distal end portion thereof is exposed to the combustion chamber 8. An ignition coil unit 26 provided at an upper portion of the cylinder head 4 is connected to the ignition plug 25. The ignition coil unit 26 generates a spark at an electrode 25a of the spark plug 25 at a predetermined timing to ignite the air-fuel mixture in the combustion chamber 8.

A fuel supply pipe 28 is connected to the fuel injection valve 24, and fuel pressure-fed from a fuel supply system (not shown) including a fuel tank, a fuel pump, and the like flows through the fuel supply pipe 28. The fuel injection valve 24 is disposed between the two intake ports 15, and has a distal end face 27 exposed to the combustion chamber 8. The fuel injection valve 24 is provided in such a manner that the distal end surface 27 faces obliquely downward, and injects fuel from the distal end surface 27 toward the crown surface 10 of the piston 5 at a specified period.

Fig. 3 is a perspective view showing details of the fuel injection valve 24. As shown in fig. 3, fuel injection valve 24 is a multi-orifice type injection valve having a plurality of nozzle orifices at its distal end face 27. The distal end surface 27 has a plurality of

nozzle orifices

24a, 24b, 24c, 24d arranged bilaterally symmetrically with respect to a shaft center 27a extending in the up-down direction. Specifically, the distal end surface 27 has a first nozzle orifice 24a located at the center of the upper portion, two second nozzle orifices 24b located at the upper position of the middle portion, two third nozzle orifices 24c located at the lower position of the middle portion, and a fourth nozzle orifice 24d located at the center of the lower portion. The first nozzle 24a and the fourth nozzle 24d are both provided on the shaft center 27 a. The second nozzle ports 24b are provided at two positions on the left and right with the axial center 27a interposed therebetween. The third nozzle ports 24c are provided at two positions on the left and right with respect to the axial center 27a, and are located at positions further away from the axial center 27a than the second nozzle ports 24 b. The fuel injected from each of the

injection ports

24a, 24b, 24c, and 24d forms a conical spray, flies in the combustion chamber 8, and is uniformly diffused in the combustion chamber 8.

As described above, in the engine 1 of the present embodiment, an intake passage (swirl port) capable of generating tumble flow in the combustion chamber 8 is used as the intake passage 15. Tumble flows play the following roles: not only the mixing of the fuel and the air but also the combustion of the mixture containing the fuel and the air is promoted. That is, when the tumble flow is collapsed as the piston 5 approaches the compression top dead center (that is, as the combustion chamber 8 is narrowed), turbulence is generated in the combustion chamber 8 based on the collapse, and combustion of the air-fuel mixture is promoted based on the generated turbulence. The larger the tumble flow velocity is, the more the turbulent energy increases, and combustion of the air-fuel mixture is promoted. In this specification, the increase in energy of the turbulent flow means an increase in kinetic energy possessed by the turbulent flow. For example, when the flow velocity of the turbulence increases or the amount of turbulence increases, the energy of the turbulence increases.

Fig. 4 is a timing chart showing a fuel injection timing. As shown in fig. 4, during normal operation of the engine 1, fuel injection from the fuel injection valve 24 is performed in two steps, i.e., an intake stroke and a compression stroke. That is, the fuel injection valve 24 performs the first injection in the first half of the intake stroke, and performs the second injection in the second half of the compression stroke. The first injection ends, for example, at 80 degrees crank angle, and the second injection ends, for example, at 325 degrees crank angle. The crank angle referred to herein is a crank angle when intake top dead center is 0 degrees (the same applies hereinafter).

The first injection performed in the first half of the intake stroke forms a uniform mixture (mixture in which fuel and air are uniformly mixed) in the combustion chamber 8 in the vicinity of compression top dead center. The second injection performed in the latter half of the compression stroke forms a mixture relatively rich in concentration of fuel (i.e., easily burned) around the ignition plug 25 in the vicinity of compression top dead center. The second injection is performed after the piston 5 is closer to the top dead center. Therefore, the volume of the combustion chamber 8 when the second injection is performed is smaller than the volume of the combustion chamber 8 when the first injection is performed.

Fig. 5 is an explanatory diagram for explaining the spray of fuel injected from the fuel injection valve 24. Specifically, fig. 5 shows the fuel spray when the fuel injection valve 24 performs the second injection described above. As shown in fig. 5, the spray F1 of the fuel injected from the first nozzle hole 24a by the second injection flies toward a chamber 40 (described later in detail) provided in the crown surface 10 of the piston 5. The fuel sprays F2 and F3 injected from the second nozzle holes 24b and the third nozzle holes 24c by the second injection fly toward the intake side inclined surface 34 (described later in detail) of the swelling portion 31 provided in the crown surface 10 of the piston 5.

As the second injection is performed, the spray F1 from the first nozzle 24a is guided upward by the circumferential surface portion 42 of the chamber 40 and moves toward the ignition plug 25, and the sprays F2 and F3 from the second nozzle 24b and the third nozzle 24c collide with the intake-side inclined surface 34 and move toward the ignition plug 25. As a result, the fuel concentration of the air-fuel mixture formed around the ignition plug 25 (the central portion of the combustion chamber 8) is richer than that of the remaining portion (the outer peripheral portion of the combustion chamber 8).

After the second injection, ignition (spark ignition) is performed by the ignition plug 25 in the latter half of the compression stroke and in the vicinity of the compression top dead center, and the air-fuel mixture is combusted. The spark ignition is performed, for example, at a crank angle of 340 degrees. In the engine 1 of the present embodiment, fuel is injected in two separate injections, and an air-fuel mixture having a relatively rich fuel concentration is formed around the spark plug 25 at the time of spark ignition, so that combustion stability is sufficiently improved.

The spark ignition in the latter half of the compression stroke (for example, when the crank angle is 340 degrees) as described above is performed at the time of the normal operation after the completion of the warm-up. On the other hand, at the time of cold start, in order to increase the temperature of the catalyst to activate the catalyst, the timing of spark ignition (ignition timing) is retarded to increase the exhaust gas temperature. When the ignition timing is retarded, the effective expansion ratio is decreased to suppress a decrease in the temperature of the exhaust gas, and therefore the exhaust gas discharged to the catalyst is maintained at a high temperature. Even in the cold operation in which the ignition timing is thus retarded, good combustion stability can be ensured by adopting the above-described injection mode in which a relatively rich air-fuel mixture is formed around the ignition plug 25.

Although not shown, the engine 1 includes a control unit that controls the engine 1 and components related to the engine 1. The control unit controls each of the fuel injection valve 24, the ignition plug 25, the variable valve timing mechanism, and the like based on various information obtained from sensors and the like.

Next, the piston 5 of the engine 1 according to the present embodiment will be described.

Fig. 6 is a perspective view of the piston 5, fig. 7 is a plan view of the piston 5, fig. 8 is a sectional view of the piston 5 taken along the line Y8-Y8 of fig. 7, fig. 9 is a sectional view of the piston 5 taken along the line Y9-Y9 of fig. 7, and fig. 10 is a sectional view of the piston 5 taken along the line Y10-Y10 of fig. 7.

In the engine 1 according to the present embodiment, the geometric compression ratio, which is the ratio of the volume of the combustion chamber 8 when the piston 5 is at the top dead center to the volume of the combustion chamber 8 when the piston 5 is at the bottom dead center, is set to 12 or more. As shown in fig. 6 to 10, the crown surface 10 of the piston 5 includes a base surface 30 perpendicular to the axial center 2a of the cylinder 2 and a raised portion 31 raised upward (toward the cylinder head 4) with respect to the base surface 30. The raised portion 31 is raised along the top surface 12 of the combustion chamber 8 so as to be higher toward the center of the piston 5. A cavity 40 recessed downward is formed in the center of the bulge portion 31 at a position corresponding to the spark plug 25.

The base surface 30 has an intake side horizontal surface 32 located on the intake side with respect to the swelling portion 31 and an exhaust side horizontal surface 33 located on the exhaust side with respect to the swelling portion 31. The intake-side horizontal surface 32 and the exhaust-side horizontal surface 33 are provided so as to be orthogonal to the axial center of the piston 5 (the axial center 2a of the cylinder 2). An intake valve pit 32a recessed downward so as not to come into contact with the intake valve 20 is provided in the intake side horizontal surface 32 at a position corresponding to the intake valve 20.

The raised portion 31 is formed in a ridge shape along the top surface 12 of the combustion chamber 8. That is, the swelling portion 31 has an intake side inclined surface 34 inclined along the intake side inclined surface 13 of the top surface 12 (the height decreases toward the intake side) and an exhaust side inclined surface 35 inclined along the exhaust side inclined surface 14 of the top surface 12 (the height decreases toward the exhaust side). The intake side inclined surface 34 is formed in a planar shape orthogonal to the valve axis 20d of the intake valve 20, and the exhaust side inclined surface 35 is formed in a planar shape orthogonal to the valve axis 21d of the exhaust valve 21.

The bulging portion 31 has an annular upper surface 36 extending along the periphery of the chamber 40 between the intake side inclined surface 34 and the exhaust side inclined surface 35, and a pair of side surfaces 37 extending obliquely from the upper surface 36 toward the outer peripheral side of the piston 5. The upper surface 36 is formed in a flat shape parallel to the base surface 30 in the central portion of the piston 5 (around the chamber 40). The pair of side surfaces 37 is formed in a conical surface shape.

The pair of side surfaces 37 respectively have: a first inclined surface 37a provided on the center side of the piston 5 and extending obliquely from the upper surface 36 toward the outer circumferential side of the piston 5; a second inclined surface 37b provided on the outer peripheral side of the piston 5 with respect to the first inclined surface 37a and inclined downward at a larger inclination angle than the first inclined surface 37 a. The first inclined surface 37a and the second inclined surface 37b are each formed in a conical shape.

Fig. 11 is an explanatory diagram for explaining the shape of the cavity 40 provided on the ridge portion 31. In the engine 1 of the present embodiment, the crown surface 10 of the piston 5 is provided with the bulge portion 31, and if the cavity 40 is not formed in the bulge portion 31, an initial flame peak, which is an outer peripheral surface of an initial flame that is burned and diffused when the ignition of the spark plug 25 is triggered, early interferes with the crown surface 10 of the piston 5. In contrast, in the present embodiment, since the chamber 40 is provided in the raised portion 31 at a position corresponding to the spark plug 25, the interference between the initial flame front and the piston 5 can be delayed.

As shown in fig. 11, the cavity 40 is formed in such a manner as to delay its interference with a hypothetical spherical surface 25c, which is a spherical surface that mimics a flame that spherically grows from an ignition point 25b at the center between the electrodes 25a of the spark plug 25. Specifically, the chamber 40 has a circular planar bottom surface portion 41 and a substantially cylindrical peripheral surface portion 42 rising upward from the peripheral edge of the bottom surface portion 41. The peripheral surface portion 42 is formed in a curved shape in cross section from the lower portion, and is smoothly connected to the bottom surface portion 41. The circumferential surface portion 42 of the cavity 40 may be formed in a shape conforming to at least a part of the virtual spherical surface 25 c.

As shown in fig. 5 to 8, a notch portion 34a is provided in an upper end portion of the intake side inclined surface 34 of the piston 5, in other words, a portion on the intake side in the peripheral edge portion of the chamber 40. The spray F1 of the fuel injected from the first nozzle hole 24a of the fuel injection valve 24 during the second injection collides with the exhaust-side circumferential surface portion 42 of the chamber 40 through the notch portion 34 a. The spray F1 having collided with the circumferential surface portion 42 is guided upward by the circumferential surface portion 42 and moves toward the electrode 25a of the spark plug 25.

As described above, in the engine 1 of the present embodiment, the geometrical compression ratio can be increased by providing the crown surface 10 of the piston 5 with the bulge portion 31, and the interference between the initial flame front and the piston 5 can be delayed by providing the cavity 40 at the position corresponding to the ignition plug 25 in the bulge portion 31, so that the flame propagation property can be improved.

In the present embodiment, as shown in fig. 8, the intake side inclined surface 34 and the exhaust side inclined surface 35 of the bulge portion 31 are formed such that the inclination angle θ 2 of the exhaust side inclined surface 35 with respect to the base surface 30 is smaller than the inclination angle θ 1 of the intake side inclined surface 34 with respect to the base surface 30, and the inclination angle difference (θ 1- θ 2) between the intake side inclined surface 34 and the exhaust side inclined surface 35 is 4 degrees or more. For example, the inclination angle θ 1 of the intake side inclined surface 34 is set to 23 degrees and the inclination angle θ 2 of the exhaust side inclined surface 35 is set to 17 degrees, so that the difference in inclination angle (θ 1- θ 2) between the two is set to 6 degrees.

Thus, the bulge portion 31 having a sufficient volume necessary for realizing a high compression ratio can be formed while setting the inclination angle θ 2 of the exhaust side inclined surface 35 to be small. The exhaust inclined surface 35 is a surface with which a tumble flow (see arrow 19 in fig. 2) flowing from the intake passage 15 to the exhaust side contacts when the tumble flow returns from the exhaust side to the intake side along the crown surface 10 of the piston 5. Therefore, the small inclination angle θ 2 of the exhaust side inclined surface 35 contributes to the reduction of the effect of the tumble flow being decelerated (blocked) by the bulge portion 31.

When the difference in inclination angles (θ 1- θ 2) between the intake-side inclined surface 34 and the exhaust-side inclined surface 35 is set to be excessively large while the volumes of the bulging portions 31 are maintained at the same level, the height of the bulging portions 31 and hence the depth H1 of the chamber 40 (the height of the peripheral surface portion 42) becomes excessively small, and the action of the peripheral surface portion 42 of the chamber 40 for guiding the fuel during the second injection is also reduced even if the fuel moves upward around the spark plug 25. In order to sufficiently exhibit such a fuel guiding function, it is necessary to sufficiently secure the height of the peripheral surface portion 42, and for this reason, it is preferable to set the difference in inclination angle between the intake side inclined surface 34 and the exhaust side inclined surface 35 to 11 degrees or less.

As shown in fig. 10, the intake side inclined surface 34 and the exhaust side inclined surface 35 are formed such that the angle θ 4 formed by the exhaust side inclined surface 35 and the side surface 37 is larger than the angle θ 3 formed by the intake side inclined surface 34 and the side surface 37, and the angle difference (θ 4- θ 3) between the angle θ 4 formed by the exhaust side inclined surface 35 and the side surface 37 and the angle θ 3 formed by the intake side inclined surface 34 and the side surface 37 is 5 degrees or more. For example, the angle θ 3 formed by the intake side inclined surface 34 and the side surface 37 is set to 162.4 degrees and the angle θ 4 formed by the exhaust side inclined surface 35 and the side surface 37 is set to 169.8 degrees, so that the difference in angle (θ 4 — θ 3) between the two is set to 7.4 degrees.

Accordingly, since the change in the angle between the exhaust side inclined surface 35 and the side surface 37 is made gentle, when the tumble flow flows over the outer peripheral portion of the crown surface 10 of the piston 5, the tumble flow can be smoothly guided from the exhaust side inclined surface 35 to the pair of side surfaces 37, and the tumble flow can be prevented from separating from the crown surface 10.

As shown in fig. 7, an intersection point of the orthogonal surface 6b, which is a surface that passes through an intersection point P1 of the valve axis 20d of the intake valve 20 and the intake-side inclined surface 34 and is orthogonal to the crank axis 6a (the axial direction of the crankshaft 6), and the ridge line S1 between the intake-side inclined surface 34 and the side surface 37 when the piston 5 is at the top dead center is assumed to be P2. The angle θ 3 formed by the intake side inclined surface 34 and the side surface 37 is an angle at which the intake side inclined surface 34 intersects the side surface 37 at the intersection point P2. More specifically, as shown in fig. 10, the angle θ 3 is an angle formed by a tangent T1 that meets the side surface 37 at the intersection point P2 and is parallel to the orthogonal surface 6b (the surface orthogonal to the crank axis 6 a) and the intake-side inclined surface 34.

Similarly, when the piston 5 is at the top dead center, the intersection point of the orthogonal plane 6c, which is a plane passing through the intersection point P3 of the valve axis 21d of the exhaust valve 21 and the exhaust-side inclined surface 35 and orthogonal to the crank axis 6a (the axial direction of the crankshaft 6), and the ridge line S2 between the exhaust-side inclined surface 35 and the side surface 37 is assumed to be P4. The angle θ 4 formed by the exhaust side inclined surface 35 and the side surface 37 is an angle at which the exhaust side inclined surface 35 and the side surface 37 intersect at the intersection point P4. More specifically, as shown in fig. 10, the angle θ 4 is an angle formed by the exhaust-side inclined surface 35 and a tangent T2 that meets the side surface 37 at the intersection point P4 and is parallel to the orthogonal surface 6c (the surface orthogonal to the crank axis 6 a).

As shown in fig. 7 and 8, the cavity 40 provided in the bump 31 is formed so that the ratio of the depth H1 of the cavity 40 to the diameter D1 of the cavity 40 (H1/D1) is 0.3 or less. For example, the ratio of the depth H1 of the cavity 40 to the diameter D1 of the cavity 40 (H1/D1) is set to 0.25 to 0.29. Further, the diameter D1 of the chamber 40 is a diameter at an upper end portion of the chamber 40, more specifically, a diameter at an upper end position of a portion of the circumferential surface portion 42 of the chamber 40 from which a rounded portion (chamfered portion) at an upper end thereof is removed.

A ratio of 0.3 or less (H1/D1) means that the chamber 40 is relatively flat (shallow). If the chamber 40 is flat, the flow in the chamber 40 is less likely to decrease. Accordingly, since the suction action toward the lower side (toward the bottom surface portion 41 side) by the chamber 40 can be reduced, when the tumble flow flows through the center portion of the crown surface 10 of the piston 5, the movement of the tumble flow toward the bottom surface portion 41 side of the chamber 40 can be suppressed, and the tumble flow can be smoothly moved from the exhaust side inclined surface 35 toward the intake side inclined surface 34.

When the ratio of the depth H1 of the chamber 40 to the diameter D1 of the chamber 40 (H1/D1) is set to be excessively small while the volume of the bulge 31 is maintained at the same level, the depth H1 of the chamber 40 (the height of the peripheral surface portion 42) becomes excessively small, and the action of the peripheral surface portion 42 of the chamber 40 for the second injection to guide the fuel, that is, the action of the fuel moving upward around the spark plug 25 is reduced. In order to sufficiently exhibit such a fuel guiding effect, it is preferable that the above-described ratio (H1/D1) is 0.16 or more.

As shown in fig. 9, the side surface 37 of the ridge portion 31 is formed such that the inclination angle θ 5 thereof is 10 degrees or less, more specifically, the inclination angle θ 5 of the side surface 37 with respect to the base surface 30 of the first inclined surface 37 a. For example, the inclination angle θ 5 of the first inclined surface 37a is set to 8 degrees to 9.2 degrees.

Thus, the first inclined surface 37a of the front surface 37 located on the center side of the piston 5 can be gently inclined, and the second inclined surface 37b having a large inclination angle (large step) can be formed on the outer peripheral side of the first inclined surface 37 a. This is advantageous in that it is necessary to form the ridge portion 31 having a sufficient volume in order to achieve a high compression ratio. Further, since the tumble flow easily flows at the center side of the piston 5 where the flow rate is large, the tumble flow decelerating action due to the bulging portion 31 can be reduced in general.

As shown in fig. 7 and 8, the intake side inclined surface 34 and the exhaust side inclined surface 35 of the bulge portion 31 are formed such that the ratio of the length L2 of the exhaust side inclined surface 35 to the length L1 of the intake side inclined surface 34 (L2/L1) is 1.25 or more in a cross section passing through the axial center of the piston 5 and orthogonal to the crank axis 6 a. For example, the ratio (L2/L1) of the length L2 of the exhaust side inclined surface 35 to the length L1 of the intake side inclined surface 34 is set to 1.33. As shown in fig. 7, the length L1 of the intake side inclined surface 34 is the length between the boundary edge portion between the intake side inclined surface 34 and the intake side horizontal surface 32 and the boundary edge portion between the intake side inclined surface 34 and the upper surface 36. Similarly, the length L2 of the exhaust side inclined surface 35 is the length between the boundary edge portion between the exhaust side inclined surface 35 and the exhaust side horizontal surface 33 and the boundary edge portion between the exhaust side inclined surface 35 and the upper surface 36.

As a result, the flow path of the tumble flow flowing on the exhaust-side inclined surface 35 becomes longer, and the tumble flow guiding function of the exhaust-side inclined surface 35 can be effectively exerted. As a result, the decelerating action of the tumble flow by the bulge portion 31 can be reduced, and the tumble flow can be maintained at a high speed.

Further, when the ratio (L2/L1) of the length L2 of the exhaust side inclined surface 35 to the length L1 of the intake side inclined surface 34 is set to be excessively large while the volume of the bulge portion 31 is maintained at the same level, the height of the bulge portion 31 and thus the depth H1 of the chamber 40 (the height of the peripheral surface portion 42) becomes excessively small, and the action of the peripheral surface portion 42 of the chamber 40 at the time of the second injection for guiding the fuel, that is, the action of moving the fuel upward toward the periphery of the ignition plug 25 is reduced. In order to sufficiently exhibit such a fuel guiding function, it is necessary to sufficiently secure the height of the peripheral surface portion 42, and for this reason, it is preferable to set the ratio (L2/L1) to 1.9 or less.

As shown in fig. 8, the bulge 31 is formed such that the ratio (H2/D2) of the height H2 of the bulge 31 to the inner diameter D2 of the cylinder 2 is 0.08 or less. The height H2 of the raised portion 31 is a height from the base surface 30 (the intake-side horizontal surface 32 and the exhaust-side horizontal surface 33) to the upper surface 36 of the crown surface 10 of the piston 5. For example, the ratio (H2/D2) of the height H2 of the bulge 31 to the inner diameter D2 of the cylinder 2 is set to 0.066 to 0.078.

This makes it possible to form the bulge portion 31 having a sufficient volume necessary for realizing a high compression ratio, and to suppress an increase in the height H2. As a result, when the tumble flow flows from the exhaust side to the intake side along the crown surface 10 of the piston 5, the swell portion 31 can suppress the tumble flow from being decelerated.

When the ratio (H2/D2) of the height H2 of the bulge 31 to the inner diameter D2 of the cylinder 2 is set to be excessively small while the volume of the bulge 31 is maintained at the same level, the height of the bulge 31 and hence the depth H1 of the chamber 40 (the height of the peripheral surface portion 42) become excessively small, and the fuel guiding action of the peripheral surface portion 42 of the chamber 40 at the time of the second injection is also reduced even if the fuel moves upward around the spark plug 25. In order to sufficiently exhibit such a fuel guiding function, it is necessary to sufficiently secure the height of the peripheral surface portion 42, and for this reason, it is preferable to set the ratio (H2/D2) to 0.056 or more.

The piston 5 is formed such that the ratio of the length L3 of the upper surface 36 to the length L4 of the second inclined surface 37b (L3/L4) is 0.8 or less in a radial cross section shown in fig. 9. For example, the ratio (L3/L4) of the length L3 of the upper surface 36 to the length L4 of the second inclined surface 37b is set to 0.34 to 0.57.

In this way, when the second inclined surface 37b located on the outer peripheral side of the piston 5 is set longer than the upper surface 36 of the central portion of the piston 5, the inclination angle of the first inclined surface 37a extending therebetween becomes smaller. Thus, the first inclined surface 37a of the side surface 37 located on the center side of the piston 5 can be gently inclined, and the second inclined surface 37b having a large inclination angle (large step) can be formed on the outer peripheral side of the first inclined surface 37 a. This is advantageous in that it is necessary to form the ridge portion 31 having a sufficient volume in order to achieve a high compression ratio. Further, since the tumble flow easily flows at the center side of the piston 5 where the flow rate is large, the deceleration of the tumble flow due to the bulging portion 31 can be suppressed in general.

When the ratio (L3/L4) between the length L3 of the upper surface 36 and the length L4 of the second inclined surface 37b is set to be excessively small while the volume of the bulge 31 is maintained at the same level, the height H2 of the bulge 31 becomes small, and the depth H1 of the cavity 40 (the height of the peripheral surface portion 42) becomes excessively small, so that the action of the peripheral surface portion 42 for the second injection to guide the fuel, that is, the action of the fuel to move upward around the spark plug 25 is reduced.

As described above, in the engine (spark ignition type internal combustion engine) 1 according to the present embodiment, the crown surface 10 of the piston 5 is provided with the bulge portion 31 including the intake-side inclined surface 34 and the exhaust-side inclined surface 35, the cavity 40 is provided in the bulge portion 31 at a position corresponding to the ignition plug 25, and the cylinder head 4 is provided with the intake passage 15 capable of generating tumble flow. The intake side inclined surface 34 and the exhaust side inclined surface 35 are formed such that the inclination angle θ 2 of the exhaust side inclined surface 35 is smaller than the inclination angle θ 1 of the intake side inclined surface 34 and the difference (θ 1- θ 2) in inclination angle between the intake side inclined surface 34 and the exhaust side inclined surface 35 is 4 degrees or more.

According to this configuration, since the crown surface 10 of the piston 5 is provided with the bulge portion 31, the volume of the combustion chamber 8 is reduced by the bulge portion 31, and the geometric compression ratio can be increased. Further, since the cavity 40 is provided in the bulge portion 31 at a position corresponding to the ignition plug 25, interference between the piston 5 and the flame can be delayed, and flame propagation can be improved.

Further, since the swelling portion 31 is formed so that the inclination angle θ 2 of the exhaust side inclined surface 35 is smaller than the inclination angle θ 1 of the intake side inclined surface 34, the tumble flow decelerating action by the swelling portion 31 can be reduced while securing a sufficient volume of the swelling portion 31 required to achieve a high compression ratio, and the fuel economy can be improved.

That is, since the exhaust side inclined surface 35 is a surface with which the tumble flow contacts when the tumble flow flows from the exhaust side to the intake side along the crown surface 10 of the piston 5, the inclination angle θ 2 of the exhaust side inclined surface 35 is small, which contributes to reducing the effect of the tumble flow being decelerated (blocked) by the bulge portion 31. As a result, the tumble flow is maintained at a high speed, the turbulent energy generated by the collapse of the tumble flow can be increased, the combustion period can be shortened, and fuel economy can be improved.

The intake side inclined surface 34 is provided so as to be orthogonal to the valve axis 20d of the intake valve 20, and the exhaust side inclined surface 35 is provided so as to be orthogonal to the valve axis 21d of the exhaust valve 21. Accordingly, the intake-side inclined surface 34 is parallel to the umbrella bottom surface 20c of the intake valve 20, and the exhaust-side inclined surface 35 is parallel to the umbrella bottom surface 21c of the exhaust valve 21, so that the flow path height of the blow flow (blowing stream) flowing from the intake passage 15 to the exhaust passage 16 can be secured at a predetermined value. That is, depending on the operating conditions of the engine 1, in order to exhaust the exhaust gas (residual exhaust gas) remaining in the combustion chamber 8, both the intake valve 20 and the exhaust valve 21 may be opened during the exhaust stroke to form a blow flow flowing from the intake passage 15 to the exhaust passage 16. At this time, if the

inclined surfaces

34 and 35 and the umbrella bottom surfaces 20c and 21c are parallel to each other as described above, the flow path height of the blowing flow can be substantially a predetermined value, and thus the progress of the blowing flow is hardly hindered. As a result, the scavenging performance of the residual exhaust gas can be improved, and the temperature of the combustion chamber 8 can be lowered, so that the occurrence of abnormal combustion due to a high compression ratio can be prevented, and the fuel economy can be improved.

[ second embodiment ]

Fig. 12 is a perspective view of a piston of a spark ignition type internal combustion engine according to a second embodiment of the present invention, fig. 13 is a plan view of the piston of the internal combustion engine, fig. 14 is a sectional view of the piston taken along line Y14-Y14 in fig. 13, and fig. 15 is a sectional view of the piston taken along line Y15-Y15 in fig. 13. The engine 51, which is a spark ignition type internal combustion engine according to the second embodiment of the present invention, is an engine having different shapes of the crown surface of the piston and the top surface of the combustion chamber from the engine 1 according to the first embodiment, and the same components as those of the engine 1 are denoted by the same reference numerals and their description is omitted.

The engine 51 according to the second embodiment also includes, similarly to the engine 1 according to the first embodiment, a cylinder 2, a piston 55 reciprocally provided in the cylinder 2, a cylinder head 4 forming a top surface 12 of a combustion chamber 8, a fuel injection valve 24 provided in the cylinder head 4 so as to face the combustion chamber 8, and an ignition plug 25 provided in the cylinder head 4 so as to face the combustion chamber 8, and the cylinder head 4 is provided with an intake passage 15 capable of generating tumble flow in the combustion chamber 8.

The geometric compression ratio of the engine 51 is set to 12 or more, and as shown in fig. 12 to 15, the crown surface 60 of the piston 55 has a base surface 30 perpendicular to the axial center 2a of the cylinder 2 and a bulging portion 61 bulging upward (cylinder head 4 side) with respect to the base surface 30. The raised portion 61 is raised along the top surface 12 of the combustion chamber 8 so as to be higher toward the center of the piston 55. A cavity 40 recessed downward is formed in the center of the bulge portion 61 at a position corresponding to the spark plug 25.

The base surface 30 has an intake side horizontal surface 62 and an exhaust side horizontal surface 63. An intake valve pit 62a recessed downward to avoid contact with the intake valve 20 is provided at a position corresponding to the intake valve 20 on the intake side horizontal surface 62.

The bulge portion 61 has an intake side inclined surface 64 inclined along the intake side inclined surface 13 of the ceiling surface 12 and an exhaust side inclined surface 65 inclined along the exhaust side inclined surface 14 of the ceiling surface 12. The intake side inclined surface 64 and the exhaust side inclined surface 65 are formed in a planar shape.

The intake side inclined surface 64 of the bulge portion 61 is provided in parallel with the intake side inclined surface 13 of the ceiling surface 12. On the other hand, the exhaust side inclined surface 65 of the rising portion 61 is provided so as not to be parallel to the exhaust side inclined surface 14 of the ceiling surface 12. Specifically, the exhaust-side inclined surface 65 of the raised portion 61 is formed such that the angle formed by the exhaust-side inclined surface 14 of the top surface 12 and the orthogonal surface orthogonal to the axial center 2a of the cylinder 2 is smaller than the angle formed by the orthogonal surface orthogonal to the axial center 2a of the cylinder 2.

The intake valve 20 is provided such that the umbrella bottom surface 20c thereof is parallel to the intake side inclined surface 13 of the ceiling surface 12, and the exhaust valve 21 is provided such that the umbrella bottom surface 21c thereof is parallel to the exhaust side inclined surface 14 of the ceiling surface 12. Specifically, the umbrella bottom surface 20c of the intake valve 20 is formed so that the angle formed by the umbrella bottom surface 20c and the orthogonal surface orthogonal to the axial center 2a of the cylinder 2 is 23 degrees, and the umbrella bottom surface 21c of the exhaust valve 21 is formed so that the angle formed by the umbrella bottom surface 21c and the orthogonal surface orthogonal to the axial center 2a of the cylinder 2 is 22 degrees.

An exhaust valve pocket 65a that is recessed downward to avoid contact with the exhaust valve 21 is provided at a position corresponding to the exhaust valve 21 on the exhaust side inclined surface 65 of the raised portion 61. The exhaust valve recess 65a is formed such that the bottom surface thereof is parallel to the umbrella bottom surface 21c of the exhaust valve 21.

The bulge portion 61 has an annular upper surface 66 along the peripheral edge of the chamber 40 between the intake side inclined surface 64 and the exhaust side inclined surface 65, and a pair of side surfaces 67 extending obliquely from the upper surface 66 toward the outer peripheral side of the piston 55. However, unlike the first embodiment, the second embodiment is different in that the pair of side surfaces 67 is not divided by the chamber 40 and is continuous on the exhaust side of the chamber 40. The upper surface 66 is formed in a flat shape parallel to the base surface 30 in the central portion of the piston 55 (around the chamber 40). The pair of side surfaces 67 is formed in a conical shape.

The pair of side surfaces 67 respectively have: a first inclined surface 67a provided at the center of the piston 55 and extending downward from the upper surface 66 to the outer periphery of the piston 55; and a second inclined surface 67b provided on the outer peripheral side of the piston 55 with respect to the first inclined surface 67a and inclined downward at a larger inclination angle than the first inclined surface 67 a. The first inclined surface 67a and the second inclined surface 67b are each formed in a conical shape.

As described above, in the engine 51 of the present embodiment, the crown surface 60 of the piston 55 is provided with the bulge portion 61 to increase the geometric compression ratio, and the cavity 40 is provided in the bulge portion 61 at a position corresponding to the ignition plug 25 to delay the interference between the initial flame front and the piston 55, thereby improving the flame propagation performance.

In the present embodiment, as shown in fig. 14, the intake side inclined surface 64 and the exhaust side inclined surface 65 of the bulge portion 61 are formed such that the inclination angle θ 2 of the exhaust side inclined surface 65 with respect to the base surface 30 is smaller than the inclination angle θ 1 of the intake side inclined surface 64 with respect to the base surface 30, and the inclination angle difference (θ 1- θ 2) between the intake side inclined surface 64 and the exhaust side inclined surface 65 is 4 degrees or more. For example, the inclination angle θ 1 of the intake side inclined surface 64 is set to 23 degrees and the inclination angle θ 2 of the exhaust side inclined surface 65 is set to 15.1 degrees, so that the difference in inclination angle (θ 1- θ 2) is set to 7.9 degrees.

As shown in fig. 13 and 14, the cavity 40 provided in the bulge 61 is formed such that the ratio of the depth H1 of the cavity 40 to the diameter D1 of the cavity 40 (H1/D1) is 0.3 or less. For example, the ratio of the depth H1 of the cavity 40 to the diameter D1 of the cavity 40 (H1/D1) is set to 0.26.

As shown in fig. 13 and 14, the intake-side inclined surface 64 and the exhaust-side inclined surface 65 of the bulge portion 61 are formed such that the ratio (L2/L1) of the length L2 of the exhaust-side inclined surface 65 to the length L1 of the intake-side inclined surface 64 is 1.25 or more in a cross section passing through the axial center of the piston 55 and orthogonal to the crank axis 6a (the axial direction of the crankshaft 6). For example, the ratio (L2/L1) of the length L2 of the exhaust side inclined surface 65 to the length L1 of the intake side inclined surface 64 is set to 1.48.

As shown in fig. 14, the bulge 61 is formed such that the ratio (H2/D2) of the height H2 of the bulge 61 to the inner diameter D2 of the cylinder 2 is 0.08 or less. For example, the ratio (H2/D2) of the height H2 of the bulge 61 to the inner diameter D2 of the cylinder 2 is set to 0.06.

The piston 55 is formed such that the ratio (L3/L4) of the length L3 of the upper surface 66 to the length L4 of the second inclined surface 67b is 0.8 or less in the radial cross section shown in fig. 15. For example, the ratio (L3/L4) of the length L3 of the upper surface 66 to the length L4 of the second inclined surface 67b is set to 0.24.

As described above, in the engine (spark ignition type internal combustion engine) 51 according to the present embodiment, the crown surface 60 of the piston 55 is provided with the bulge portion 61 including the intake-side inclined surface 64 and the exhaust-side inclined surface 65, the cavity 40 is provided in the bulge portion 61 at a position corresponding to the ignition plug 25, and the intake passage 15 capable of generating tumble flow is provided in the cylinder head 4. Further, the intake side inclined surface 64 and the exhaust side inclined surface 65 are formed as follows: the inclination angle theta 2 of the exhaust side inclined surface 65 is smaller than the inclination angle theta 1 of the intake side inclined surface 64, and the difference in inclination angle (theta 1-theta 2) between the intake side inclined surface 64 and the exhaust side inclined surface 65 is 4 degrees or more.

According to this structure, the geometric compression ratio can be improved based on the bulge portion 61 formed on the crown surface 60 of the piston 55, and the flame propagation property can be improved based on the chamber 40 formed in the bulge portion 61.

Further, since the rising portion 61 is formed so that the inclination angle θ 2 of the exhaust side inclined surface 65 is smaller than the inclination angle θ 1 of the intake side inclined surface 64, the tumble flow decelerating action by the rising portion 61 can be reduced while securing a sufficient volume of the rising portion 61 necessary for achieving high compression, and the fuel economy can be improved.

That is, since the exhaust side inclined surface 65 is a surface with which the tumble flow contacts when the tumble flow flows from the exhaust side to the intake side along the crown surface 60 of the piston 55, if the inclination angle θ 2 of the exhaust side inclined surface 65 is small, the effect of decelerating (hindering) the tumble flow by the bulge portion 61 is reduced. Accordingly, since the tumble flow is maintained at a high speed, the energy of the turbulent flow generated by the tumble flow breakup can be increased, the combustion period can be shortened, and the fuel economy can be improved.

The present invention is not limited to the illustrated embodiments, and various improvements and design changes can be made without departing from the scope of the present invention.

Examples

The inclination angles of the intake side inclined surface 34 and the exhaust side inclined surface 35 of the bulging portion 31 of the piston 5 of the first embodiment were variously changed, and a simulation analysis was performed on the engine 1 including the piston 5. Specifically, the engine 1 including the piston 5 was subjected to simulation analysis under the same operating conditions while variously changing the difference in inclination angle (θ 1- θ 2) between the intake-side inclined surface 34 and the exhaust-side inclined surface 35 while maintaining the volume of the bulge portion 31 of the piston 5 at the same level, and the turbulence energy of the air-fuel mixture in the combustion chamber 8 at the top dead center of the piston 5 was examined.

Fig. 16 is a graph obtained by the above simulation analysis, and shows the relationship between the difference in inclination angle (θ 1- θ 2) between the intake-side inclined surface 34 and the exhaust-side inclined surface 35 and the turbulent energy of the air-fuel mixture in the combustion chamber 8 at the top dead center of the piston 5.

As an example of the conventional technology, an engine including a conventional piston, that is, a piston having an intake side inclined surface 34 and an exhaust side inclined surface 35 whose inclination angles are substantially equal to each other is used, and as an example, an engine including a piston 5 according to the present embodiment, that is, a piston having an inclination angle difference (θ 1- θ 2) between the intake side inclined surface 34 and the exhaust side inclined surface 35 of 4 degrees or more is used. Specifically, fig. 16 shows a black square diagram showing a result obtained when the inclination angle θ 1 is set to 23 degrees and the inclination angle θ 2 is set to 22 degrees as an example of the conventional technique. In addition, the results obtained when the inclination angle θ 1 was set to 23 degrees and the inclination angle θ 2 was set to 18 degrees and the results obtained when the inclination angle θ 1 was set to 23 degrees and the inclination angle θ 2 was set to 17 degrees are shown in white quadrangles as examples. Further, according to the above-described drawings, a line Z showing a relationship between the difference in inclination angle between the intake side inclined surface and the exhaust side inclined surface and the turbulent energy is also shown.

As shown by the line Z in fig. 16, as the difference in the inclination angle between the intake-side inclined surface 34 and the exhaust-side inclined surface 35 increases, the turbulent flow energy also increases. The line Z has an inflection point at a position where the difference in the inclination angle is about 4 degrees, and the turbulent flow energy is increased by at least 10% as compared with the engine of the conventional example. From the results, it is understood that the tumble flow decelerating action can be reduced and the turbulent flow energy can be effectively increased by setting the difference in the inclination angle between the intake side inclined surface 34 and the exhaust side inclined surface 35 to 4 degrees or more (see the broken line in fig. 16).

< summary of the embodiments >

The above embodiments are summarized as follows.

A spark ignition type internal combustion engine includes: a cylinder; a piston disposed in the cylinder so as to be capable of reciprocating; a cylinder head provided on the cylinder and forming a ridge-shaped combustion chamber together with an inner peripheral surface of the cylinder and a crown surface of the piston; and an ignition plug provided to the cylinder head so as to face the combustion chamber. A crown surface of the piston is provided with a bulge portion having an intake side inclined surface and an exhaust side inclined surface along a top surface of the combustion chamber, a chamber depressed downward is provided at a position corresponding to the ignition plug in the bulge portion, the cylinder head is provided with an intake passage capable of generating tumble flow in the combustion chamber, and the intake side inclined surface and the exhaust side inclined surface are formed as follows: the inclination angle of the exhaust side inclined surface is smaller than that of the intake side inclined surface, and the difference in inclination angle between the intake side inclined surface and the exhaust side inclined surface is 4 degrees or more.

According to this configuration, since the crown surface of the piston is provided with the bulge portion, the volume of the combustion chamber is reduced by the bulge portion, and the geometric compression ratio can be increased. Further, since the chamber is provided at a position corresponding to the spark plug in the bulge portion, interference between the piston and the flame can be delayed, and flame propagation can be improved.

Further, since the rising portion is formed so that the inclination angle of the exhaust side inclined surface is smaller than the inclination angle of the intake side inclined surface, the tumble flow decelerating action due to the rising portion can be reduced while securing a sufficient volume of the rising portion required to achieve a high compression ratio, and the fuel economy can be improved.

That is, since the exhaust side inclined surface is a surface with which the tumble flow contacts when the tumble flow flows from the exhaust side to the intake side along the crown surface of the piston, the inclination angle of the exhaust side inclined surface is small, which contributes to reducing the effect of the tumble flow being decelerated (hindered) by the bulge portion. As a result, the tumble flow is maintained at a high speed, the turbulent energy generated by the collapse of the tumble flow can be increased, the combustion period can be shortened, and fuel economy can be improved.

Preferably, the intake side inclined surface is provided so as to be orthogonal to a valve axis of the intake valve, and the exhaust side inclined surface is provided so as to be orthogonal to a valve axis of the exhaust valve.

According to this configuration, the intake-side inclined surface and the umbrella bottom surface of the intake valve are parallel to each other, and the exhaust-side inclined surface and the umbrella bottom surface of the exhaust valve are parallel to each other, so that the flow path height of the blow flow from the intake port to the exhaust port can be maintained at a substantially predetermined value. That is, depending on the operating conditions of the internal combustion engine, in order to exhaust the exhaust gas (residual exhaust gas) remaining in the combustion chamber, both the intake valve and the exhaust valve may be opened during the exhaust stroke to form a blow flow flowing from the intake port to the exhaust port. In this case, if the inclined surfaces are parallel to the bottom surface of the umbrella part as described above, the height of the flow path of the blowing flow can be set to a substantially predetermined value, and therefore, the progress of the blowing flow is less likely to be hindered. As a result, the scavenging performance of the residual exhaust gas can be improved, and the temperature of the combustion chamber can be reduced, so that the occurrence of abnormal combustion due to a high compression ratio can be prevented, and the fuel economy can be improved.

The structures capable of producing the above effects can increase the geometric compression ratio of the cylinder. Therefore, the geometric compression ratio of the cylinder can be set to, for example, 12 or more.

Industrial applicability

As described above, according to the present invention, in a spark ignition type internal combustion engine in which a crown surface of a piston is provided with a bulge portion and a chamber is provided at a position corresponding to an ignition plug in the bulge portion, a tumble flow decelerating action due to the bulge portion can be reduced, and fuel economy can be improved.

Claims

1. A spark ignition type internal combustion engine characterized by comprising:

a cylinder;

a piston disposed in the cylinder so as to be capable of reciprocating;

a cylinder head provided on the cylinder and forming a ridge-shaped combustion chamber together with an inner peripheral surface of the cylinder and a crown surface of the piston; and

an ignition plug provided to the cylinder head so as to face the combustion chamber; wherein the content of the first and second substances,

the spark plug is disposed at a central portion of a top surface of the combustion chamber,

a crown surface of the piston is provided with a bulging portion having an intake side inclined surface and an exhaust side inclined surface along a top surface of the combustion chamber,

a chamber depressed downward is provided in a central portion of the bulging portion at a position corresponding to the spark plug,

an intake passage capable of generating tumble flow in the combustion chamber is provided in the cylinder head,

the intake side inclined surface and the exhaust side inclined surface are formed in such a manner that: the inclination angle of the exhaust side inclined surface is smaller than that of the intake side inclined surface, and the difference in inclination angle between the intake side inclined surface and the exhaust side inclined surface is 4 degrees or more,

the chamber has a bottom surface portion having a circular planar shape and a substantially cylindrical peripheral surface portion rising upward from a peripheral edge of the bottom surface portion.

2. The spark ignition type internal combustion engine according to claim 1, characterized in that:

the intake side inclined surface is provided so as to be orthogonal to a valve axis of the intake valve, and the exhaust side inclined surface is provided so as to be orthogonal to a valve axis of the exhaust valve.

3. The spark ignition type internal combustion engine according to claim 1 or 2, characterized in that:

the geometric compression ratio of the cylinder is more than 12.